Pay-as-you-go or pay-per-use business models have been used in many areas of commerce, from cellular telephones to commercial laundromats. In developing a pay-as-you go business, a service provider, for example, a cellular telephone provider, offers the use of hardware (a cellular telephone) at a lower-than-market cost in exchange for a commitment to remain a subscriber to their network. In this specific example, the customer receives a cellular phone for little or no money in exchange for signing a contract to become a subscriber for a given period of time. Over the course of the contract, the service provider recovers the cost of the hardware by charging the consumer for using the cellular phone.
One possible pay-as-you-go business model measures use based on some measurable unit, such as time, CPU cycles, disk access, data packets transferred, etc. The unit for measurement, may, in some cases, be quite fine, for either technical or business reasons. For example, time may be measured in microseconds because it is a convenient unit for the operating system or other metering circuit to access. Since metering data may be tracked in volatile memory, the system may be required to periodically store the metering data in a non-volatile memory should the power be lost or another catastrophic loss of data occur in volatile memory. However, non-volatile memory, such as disk drive, may be too slow to write data at each “clock tick.” Similarly, other non-volatile memory, such as EEPROM, may have a restricted number of write cycles that does not allow writing each “clock tick” to memory over the life of the product. Even when using a fast non-volatile memory, such as battery-backed RAM, encryption processes for securing the data may be too slow to allow writing data as fast as it is updated.
Since each of the above deficiencies in writing metering data to non-volatile memory results in storing the data a rate slower than the metering data is generated, some quantization error may occur between the actual metered data and that written to non-volatile memory. This effect is most evident in the case when the computer shuts down or restarts without writing the current metering data to non-volatile memory. Over time, this quantization error may accrue to the benefit of either the subscriber or the service provider, perhaps substantially. In some cases, the benefit to one party could be so substantial as to invite fraud by the subscriber on one hand or cause subscriber dissatisfaction on the other.